Biomedical subjects

U A Brinkman

Publications and source records attributed to U A Brinkman.

At least 19 recordsLinked to original sources

PubMed2001

Monofluorinated polycyclic aromatic hydrocarbons as internal standards to monitor trace enrichment and desorption of their parent compounds during solid-phase extraction.

Solid-phase extraction (SPE) is an established sample-preparation technique for clean-up procedures of polycyclic aromatic hydrocarbons (PAHs). The suitability of monofluorinated polycyclic aromatic hydrocarbons (F-PAHs) as a novel set of internal standards, was tested for two widely used SPE sorbents, octyl-bonded silica and styrene-divinylbenzene copolymer. The elution profiles of eight F-PAHs and their parent PAHs, taken from the priority pollutant list of the US-Environmental Protection Agency, were compared for demineralized water and waste water. In both instances, the match of the elution profiles was exceptionally close. The eight F-PAHs and the corresponding PAHs were determined by reversed-phase liquid chromatography using acetonitrile-water gradient elution with UV detection at 254 nm. The UV spectra of the F-PAHs show a small bathochromic shift compared with the parent PAHs.

Chromatography, Liquid↗

PubMed2001

Detection of nonderivatized peptides in capillary electrophoresis using quenched phosphorescence.

A capillary electrophoresis detection technique for (small) peptides is presented, i.e. quenched phosphorescence, a method that is generally applicable and does not require chemical derivatization. For this purpose, a novel phosphorophore, 1-bromo-4-naphthalenesulfonic acid (BrNS), was synthesized. BrNS has sufficient water solubility and provides strong phosphorescence at room temperature over a wide pH range. The detection is based on the dynamic quenching of the BrNS phosphorescence background signal by electron transfer from the amino group of the peptides at pH 9.5-10. For the di- and tripeptides Val-Tyr-Val, Val-Gly-Gly, Ala-Ser, Gly-Asn, Gly-Ala, and Gly-Tyr, detection limits in the range of 5-20 microg/L were obtained. The novel technique is even a good alternative for the (limited) group of peptides containing tyrosine and, thus, exhibiting native fluorescence as well as strong UV absorption: using Gly-Tyr, Val-Tyr-Val, methionine enkephalin, and human angiotensin II as test compounds, quenched phosphorescence detection was found to compare favorably with absorption detection at 190- and 266-nm laser-induced fluorescence detection, as performed with a recently developed, small-size, quadrupled Nd:YAG laser.

Angiotensin II↗

PubMed2001

On-line identification method in column liquid chromatography: UV resonance Raman spectroscopy.

Ultraviolet resonance Raman spectroscopy (RRS) is presented as a novel identification tool for conventional-size column liquid chromatography (LC). The on-line coupling was made using a standard Z-shaped flow cell. A continuous-wave frequency-doubled argon ion laser operating at a wavelength of 244 nm was used for excitation. "On-the-fly" resonance Raman spectra of four model compounds, fluorene, phenanthrene, fluoranthene, and pyrene, were recorded after a standard acetonitrile/water reversed-phase LC separation. When applying a large-volume-injection procedure (32 mL), detection limits were at the nanogram per milliliter level. The results indicate that UV-RRS gives detailed spectral information at an appropriate sensitivity level so that coupling with LC becomes feasible.

Journal Article↗

PubMed2001

Determination of isoflavone glucoside malonates in Trifolium pratense L. (red clover) extracts: quantification and stability studies.

Isoflavones, their glucosides and their glucoside malonates were determined in red clover leaf extracts using reversed-phase LC coupled to atmospheric pressure chemical ionisation mass spectrometry (APCI-MS), UV and fluorescence detectors and the stability of the malonates was investigated. Extracts can be stored at least 1-2 weeks at -20 degrees C without loss of malonates. In LC-separated fractions the malonates are most stable when stored at low temperature after evaporation to dryness. The concentrations of eight major isoflavones ranged from 0.04 to 5 mg/g leaves.

Atmospheric Pressure↗

PubMed2001

Quantititative determination of glycosylated and aglycon isoprenoid cytokinins at sub-picomolar levels by microcolumn liquid chromatography combined with electrospray tandem mass spectrometry.

Microcolumn liquid chromatography (microLC) combined with electrospray tandem mass spectrometry is used for the determination of intact glycosylated cytokinins and the corresponding aglycons at picomole and sub-picomole levels in plant tissue. Routine analysis was done on C8-bonded silica using a methanol-water gradient. Data acquisition was performed by multiple reaction monitoring. Quantification was carried out by using isotopically labelled analogues and applying linear regression to the response factor versus concentration data. For routine analysis a calibration range from 0.5 to 10 pmole injected on-column was used. The limits of detection ranged from 50 to 100 fmole injected on-column. The microLC procedure was used to analyse plant tissue extracts from transgenic homozygote and hemizygote as well as wild-type Nicotiana tabacum species, and cauliflower samples. The data were compared with results obtained by conventional immunoassay and a satisfactory correlation was found. Validation data are presented.

Chromatography, Affinity↗

PubMed2001

Application of microcolumn liquid chromatography and capillary electrophoresis with flame photometric detection for the screening of degradation products of chemical warfare agents in water and soil.

Microcolumn liquid chromatography (microLC) and capillary electrophoresis (CE) coupled on-line with flame photometric detection (FPD) have been used for the screening of polar breakdown products of chemical warfare agents in water and soil samples, provided during Official Proficiency Tests organized by the Technical Secretariat of the Organization for the Prohibition of Chemical Weapons. CE-FPD is shown to be a powerful and rapid method for the determination of alkylphosphonic acids, which are the breakdown products of organophosphorus nerve agents. Gradient elution microLC-FPD is more sensitive and robust but less rapid in the determination of these compounds. In addition, microLC-FPD can be applied to screen for hydrolysis products of sulfur mustard and its analogues. Both methods can be applied without prior derivatization and are extremely selective. In order to unambiguously identify the relevant compounds, electrospray ionization (tandem) mass spectrometry, gas chromatography-mass spectrometry and nuclear magnetic resonance spectrometry were applied.

Chemical Warfare Agents↗

PubMed2001

Dialysis-solid-phase extraction combined on-line with non-aqueous capillary electrophoresis for improved detectability of tricyclic antidepressants in biological samples.

Dialysis-solid-phase extraction (SPE) sample pretreatment is combined on-line with non-aqueous capillary electrophoresis for the determination of tricyclic antidepressants in urine and serum. After clean-up and enrichment, the water is removed from the sample matrix and the analytes are eluted from the cartridge by means of an organic solvent. Next, the eluate is transported to the capillary and the injection is performed electrokinetically. This injection, which does not suffer from an adverse sample matrix effect because of the SPE step, results in further analyte concentration. The detection limits are in the 0.02-0.1 microg/ml range and the day-to-day repeatabilities are between 2.5 and 9.5%, which is quite satisfactory.

Antidepressive Agents, Tricyclic↗

PubMed2001

Automated determination of fatty acid methyl ester and cis/trans methyl ester composition of fats and oils.

The determination of the fatty acid composition (as methyl esters, FAMEs) of fats and oils and their cis/trans (CTME) distribution requires a simple, but manual and time-consuming sample preparation. The so-called BF3 method is often the preferred procedure. Because FAME/CTME analyses are encountered very frequently in the food industry, an automated, robot-based alternative is proposed which uses the sodium methylate procedure. After sample weighing and the (manual) addition of heptane (2 min), a XYZ robotic autosampler is used for all remaining work, which includes reagent addition, agitation, sample settling and the final injection into the gas chromatograph (10 min). The performance of the sodium methylate and BF3 methods are compared by analysing some 30 oil and fat samples. The novel procedure is much faster (less than 15 min versus ca. 1 h) and manual sample handling is drastically decreased. The experimental results obtained with the two methods frequently are the same, while small differences can be explained by (known) differences of the two methods in the conversion of minor oil/fat constituents, such as free fatty acids, wax esters and sterol esters. In case of FAME analyses, a hot injection is to be preferred over a cold injection. The RSDs of the peak areas were 1.5% for the major fatty acids to 11% for peaks that were just above the noise level. The detection limit were approximately 0.03%.

Automation↗

PubMed2001

Simple, non-moving modulation interface for comprehensive two-dimensional gas chromatography.

A simple, non-moving dual-stage CO2 jet modulator is described, which cools two short sections of the front end of the second-dimension column of a comprehensive two-dimensional gas chromatograph. A stream of expanding CO2 is sprayed directly onto this capillary column to trap small fractions eluting from the first-dimension column. Remobilization of the trapped analytes is performed by direct heating by the GC oven air. Installation, maintenance and control of the modulator is simple. Focusing and remobilization of the fractions is a very efficient process, as the bandwidths of the re-injected pulses are less than 10 ms. As a result, alkane peaks eluting from the second-dimension column have peakwidths at the baseline of only 120 ms.

Carbon Dioxide↗

PubMed2001

Liquid-core waveguide technology for coupling column liquid chromatography and Raman spectroscopy.

The on-line coupling of liquid chromatography (LC) and Raman spectroscopy (RS) via an entirely plastic liquid-core waveguide (LCW) was optimized in terms of excitation wavelength of the laser, especially in relation to the fluorescence background, and the length of the LCW. Excitation at 632.8 nm (He-Ne laser) was found to be a good compromise between a wavelength long enough to strongly reduce the fluorescence background and, on the other hand, short enough to avoid (re)-absorption of laser light and Raman signals by H2O in LCWs of considerable length. This conclusion is supported by a theoretical discussion on the optimization of LCW lengths as function of the excitation wavelength for H2O and 2H2O. When using the He-Ne laser the optimum length is approximately 50 cm for H2O; this corresponds to a detection cell volume of 19 microl for an LCW of 220 microm I.D., which is fully compatible with conventional-size LC. The influence of an organic modifier, usually necessary for reversed-phase LC, on the free spectral window was evaluated. The potential applicability of LC-LCW-RS was shown for a mixture of adenosine 5'-monophosphate (AMP), guanosine 5'-monophosphate (GMP) and uridine 5'-monophosphate (UMP), utilizing an aqueous eluent without the addition of a modifier. Improved detectability was achieved by using the stopped-flow mode and applying a large-volume-injection procedure (injection volume: 200 microl). Under these conditions, the limit of identification for AMP, GMP and UMP was in the 0.1-0.5-mg/ml range.

Adenosine Monophosphate↗

PubMed2001

Miniaturized automated matrix solid-phase dispersion extraction of pesticides in fruit followed by gas chromatographic-mass spectrometric analysis.

In this study a simple and fast miniaturized automated matrix solid-phase dispersion method for the sample preparation and quantitative extraction of pesticides was developed and evaluated. Only 25 mg of sample and 100 microl of organic solvent were used per analysis for this new miniaturized set-up. The extracts were subsequently analysed by GC-MS without any further purification. The method was optimized for oranges and tested for the determination of a variety of organophosphorus pesticides and a pyrethroid at concentration levels below the maximum residue levels set by the European Union and authorities in The Netherlands. The limits of detection were 4-90 microg/kg. The recoveries for pesticides in orange were 83-118% and the relative standard deviations for the total procedure were 10-13% (n=4) at the limit of quantification. The feasibility of the developed method for apple, pear and grapes was also studied. Equally good results were obtained, but for apple the washing step should be omitted.

Automation↗

PubMed2001

Screening for transformation products of pesticides using tandem mass spectrometric scan modes.

The applicability of tandem mass spectrometric (MS-MS) scan modes such as constant neutral-loss and precursor-ion scanning to screen for unknown transformation products (TPs) of pesticides at environmentally relevant concentrations (low-microng/l level) is studied. The selection of the MS-MS scan modes is based on the product-ion scan of the parent pesticide, and TPs are detected which are unaltered in the part of the structure concerned. The screening approach is applied to a surface water sample spiked with atrazine and three known TPs at a level of 3 microg/l to study the possibility to extract the TPs from the total ion chromatogram. Next, the approach is used to identify unknown TPs formed after (bio)degradation of two test compounds, fenchlorazole-ethyl (FCE) and furathiocarb (FTC). By using the precursor-ion scan mode, two TPs were detected after biodegradation of FCE, fenchlorazole-methyl and fenchlorazole; in surface water only fenchlorazole was found. The constant neutral-loss scan mode was used to identify carbofuran as TP of FTC. The added value of the proposed procedure is the increased selectivity at the cost of sensitivity. Best results are, therefore, obtained for samples which contain large amounts of matrix constituents.

Pesticides↗

PubMed2001

Mass spectrometric confirmation criterion for product-ion spectra generated in flow-injection analysis. Environmental application.

The suitability of a confirmation criterion recently recommended in the Netherlands for gas chromatography with mass spectrometric detection (GC-MS), was evaluated for flow-injection analysis (FIA) with atmospheric pressure chemical ionisation MS-MS detection. The main feature of the criterion is that the relative ion abundances of the four diagnostic ions are taken into account. That is, for lower-intensity peaks, relative standard deviations may be higher; this is an advantage with chemical ionisation MS procedures. A series of triazines and their degradation products were used as test compounds. Tap and surface water samples spiked at 0.33 microg/l were analysed by means of a selected reaction monitoring MS-MS procedure. For all analytes but hydroxysimazine (3 transitions), 4-9 transitions could be selected which invariably met the demands of the criterion. Some of the transitions used originate from the 37Cl isotopic mass of the parent compounds which provides additional structural information. Data for twenty surface water samples analysed by means of FIA-MS-MS as well as GC-MS and liquid chromatography with diode array UV and MS-MS detection gave essentially the same results over the 0.1-1.0 microg/l range. In two samples desethylatrazine was reported by FIA-MS-MS whereas this compound was not detected by GC-MS. For a first test, this is a promising result.

Flow Injection Analysis↗

PubMed2001

Characterisation of fatty acids in biological oil samples using comprehensive multidimensional gas chromatography.

Comprehensive multidimensional gas chromatography can adequately resolve very complex mixtures of analytes such as the fatty acid mixtures which are contained in, e.g., fish and vegetable oils. Well-ordered patterns are obtained in the two-dimensional separation plane which can be used to tentatively identify peaks when no standard is available. The technique which can also be used for quantification, i.e., quantitative ratio analysis, should be especially useful for fingerprinting purposes. Unravelling the composition of complex mixtures such as fish oils appears to be highly rewarding.

Chromatography, Gas↗

PubMed2001

Determination of alkylphosphonic acids by microcolumn liquid chromatography with gradient elution coupled on-line with flame photometric detection.

Microcolumn liquid chromatography with gradient elution and on-line flame photometric detection has been used for the selective and rapid determination of non-volatile alkylphosphonic acids, which are hydrolysis products of nerve agents, in aqueous samples. A make-up of water was used to maintain stable introduction of the eluent during a gradient run. The detection limits are strongly dependent on quenching, which is determined by the mass flow of methanol in the eluent. Large-volume injections of 100 microl of aqueous solutions of short- and long-chain alkylphosphonic acids resulted in detection limits in the range 6-800 ng/ml. The repeatability of the retention times and analyte response - peak area or peak height were 0.7-0.9% and 4-11%, respectively. The method was successfully applied to a local tap water sample and an aqueous soil extract.

Chromatography, Liquid↗

PubMed2001

Laser-induced fluorescence detection at 266 nm in capillary electrophoresis. Polycyclic aromatic hydrocarbon metabolites in biota.

The separation of five phenolic polycyclic aromatic hydrocarbon metabolites (hydroxy-PAHs) has been performed by cyclodextrin-modified micellar electrokinetic chromatography (CD-MEKC) using a 30 mM borate buffer (pH 9.0) containing 60 mM sodium dodecyl sulfate and varying concentrations of gamma-cyclodextrin (gamma-CD). A concentration of 12.5 mM gamma-CD was found to provide a baseline separation of the five hydroxy-PAHs. We applied conventional fluorescence and laser-induced fluorescence (LIF) detection, using a new, small-size, quadrupled Nd-YAG laser emitting at 266 nm. The best limits of detection, in the low ng/ml range, were achieved using LIF detection. For all analytes, linearity was observed up to ca. 100 ng/ml. As an application, conjugated pyrene metabolites in hepatopancreas samples from the terrestrial isopods Oniscus asellus and Porcellio scaber were separated and detected. Finally, flatfish bile samples from individuals exposed to polluted sediment or crude oil, which were part of an interlaboratory study, were analyzed by CD-MEKC with conventional fluorescence and LIF detection to determine the 1-hydroxypyrene concentrations.

Animals↗

PubMed2001

Measurement of volatile organic compounds in sediments of the Scheldt estuary and the Southern North Sea.

The concentrations and distribution of 13 priority volatile organic compounds (VOCs) were determined in sediments of the Scheldt estuary and the Belgian continental shelf, using a modified Tekmar LSC 2000 purge-and-trap system coupled to GC-MS. The method allows a sample intake of up to 50 g wet weight and detection limits are between 0.003 ng/g (tetrachloromethane) and 0.16 ng/g (m- and p-xylene). The repeatability (n = 5) varied between 4% (benzene) and 17% (toluene) and the recoveries ranged from 59% (1,1-dichloroethane) to 99% (tetrachloromethane). Because of the nature of the contaminants, special attention was paid to analyte losses and contamination of the samples during storage aboard the research vessel. Spiked sediment samples were prepared in the laboratory and stored aboard under the same conditions as the environmental samples. The recoveries for these samples varied between 94 and 130%, which suggests that storage had no adverse effect on the samples. No detectable VOC concentrations were found for most of the sampling stations. However, in the Antwerp harbour area, significant concentrations of VOCs were found. The sorption behaviour as predicted from laboratory equilibrium partitioning experiments gives an indication of the in situ partitioning behaviour of VOCs. Although VOCs in sediments should, in general, not be regarded as a major problem in the marine environment, high local concentrations may be a cause of concern.

Geologic Sediments↗

PubMed2001

Gross fluxes and estuarine behaviour of pesticides in the Scheldt estuary (1995-1997).

As part of the Fluxes of Agrochemicals into the Marine Environment (FAME) project, the gross fluxes of selected pesticides (i.e. the herbicides atrazine, simazine, alachlor and metolachlor, the atrazine degradation product desethylatrazine, the insecticide dichlorvos and the antifouling agent Irgarol 1051) transported by the river Scheldt and the Canal Ghent-Terneuzen were determined from March 1995 through February 1997. In general, the observed temporal trends were related to the application period of the pesticides, except for metolachlor for which elevated concentrations were observed in the winter of 1995-1996. Relatively large gross fluxes were found for desethylatrazine compared with its parent compound. A study on the estuarine behaviour of pesticides showed distinct differences between the compound classes. The mixing plots of the organophosphorus insecticides dichlorvos and diazinon revealed clear evidence of estuarine loss processes which agrees with their low DT50 values reported for water/sediment systems, their relatively high Henry's law constants and, for diazinon, its relatively high Koc value. The mixing plots of the acetanilides alachlor and metolachlor were strongly influenced by an additional direct emission into the estuary, which was evident from a maximum in dissolved concentration near a salinity of 10@1000. An apparent conservative behaviour was observed for the triazine compounds atrazine and Irgarol 1051. This was in contrast to simazine, which showed an apparent non-conservative behaviour. However, the time profiles of the riverine concentrations of simazine did not exclude that the observed curvature was solely caused by estuarine losses; therefore, additional modelling is required. In a follow-up study a suitable hydrological model of the Scheldt estuary was constructed; the results will be presented in a forthcoming paper (Steen, R.J.C.A., Evers, E.H.G., Van Hattum, B., Cofino, W.P. and Brinkman, U.A.Th. Net fluxes of pesticides from the Scheldt estuary into the North Sea: a model approach. Environmental Pollution, submitted.

England↗